measuring years through the Antarctica icesheets

From: Hon Wai Lai <honwai@bumble.u-net.com>
Date: Fri Nov 25 2005 - 16:40:55 EST

How do scientists measure years through the Antarctica icesheets?
 
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http://news.bbc.co.uk/1/hi/sci/tech/4467420.stm
 
CO2 'highest for 650,000 years'

By Richard Black
Environment Correspondent, BBC News website
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Current levels of the greenhouse gases carbon dioxide and methane in the
atmosphere are higher now than at any time in the last 650,000 years.

That is the conclusion of new European studies looking at ice taken from
3km below the surface of Antarctica.

The scientists say their research shows present day warming to be
exceptional.

Other research, also published in the journal Science, suggests that sea
levels may be rising twice as fast now as in previous centuries.

Treasure dome

The evidence on atmospheric concentrations comes from an Antarctic
region called Dome Concordia (Dome C).

  
 
Over a five year period commencing in 1999, scientists working with the
European Project for Ice Coring in Antarctica (Epica) have drilled
3,270m into the Dome C ice, which equates to drilling nearly 900,000
years back in time.

Gas bubbles trapped as the ice formed yield important evidence of the
mixture of gases present in the atmosphere at that time, and of
temperature.

"One of the most important things is we can put current levels of carbon
dioxide and methane into a long-term context," said project leader
Thomas Stocker from the University of Bern, Switzerland.

"We find that CO2 is about 30% higher than at any time, and methane 130%
higher than at any time; and the rates of increase are absolutely
exceptional: for CO2, 200 times faster than at any time in the last
650,000 years."

Stable relationship

Last year, the Epica team released its first data. The latest two papers
analyse gas composition and temperature dating back 650,000 years.

This extends the picture drawn by another Antarctic ice core taken near
Lake Vostok which looked 440,000 years into the past.

The extra data is crucial because around 420,000 years there appears to
have been a significant shift in the Earth's long-term climate patterns.

Before and after this date, the planet went through 100,000 year cycles
of alternating cold glacial and warm interglacial periods.

  
 
But around the 420,000 year mark, the precise pattern changed, with the
contrast between warm and cold conditions becoming much more marked.

The Dome C core gives data from six cycles of glaciation and warming;
two from before this change, four from after.

"We found a very tight relationship between CO2 and temperature even
before 420,000 years," said Professor Stocker.

"The fact that the relationship holds across the transition between
climatic regimes is a very strong indication of the important role of
CO2 in climate regulation."

Epica scientists will now try to extend their analysis further back in
time.

Water rise

Another study reported in the same journal claims that for the last 150
years, sea levels have been rising twice as fast as in previous
centuries.

Using data from tidal gauges and reviewing findings from many previous
studies, US researchers have constructed a new sea level record covering
the last 100 million years.

They calculate the present rate of rise at 2mm per year.

"The main thing that's changed since the 19th Century and the beginning
of modern observation has been the widespread increase in fossil fuel
use and more greenhouse gases," said Kenneth Miller from Rutgers
University.

The Intergovernmental Panel on Climate Change, the body which collates
scientific evidence for policymakers, concludes that sea level rose by
1-2mm per year over the last century, and will rise by a total of
anything up to 88cm during the course of this century.

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Received on Fri Nov 25 16:44:26 2005

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